If you’ve ever flown into San Francisco, you might have gotten a little warning announcement from your captain about seeing another plane out the windows.

You see, San Francisco has two parallel runways that are 750 ft apart, which I believe is the minimum distance allowed between runways. As you’re landing, it sometimes appears as if another airplane is coming right at you, and it makes some people nervous. You might get nervous if you saw something like this or this, too. Maybe this will put it in a little better perspective.